Learning Objectives
- Understand slow and fast motion
- Learn about speed and its measurement
- Understand distance-time graphs
- Know about measurement of time
Key Concepts
Speed
Speed: The distance covered by an object in unit time.
Speed = Distance ÷ Time
SI unit of speed: metre per second (m/s). Also expressed as km/h (kilometres per hour).
Conversion: 1 km/h = 5/18 m/s; 1 m/s = 18/5 km/h
Types of Motion
- Uniform motion: Object covers equal distances in equal intervals of time. Speed is constant.
- Non-uniform motion: Object covers unequal distances in equal intervals of time. Speed changes.
Measurement of Time
Basic unit of time: Second (s). Other units: minute (60 s), hour (3600 s).
Periodic motion: Motion that repeats at regular intervals (pendulum, clock hands).
Simple pendulum: A small weight (bob) suspended from a fixed point by a thread. One oscillation = one complete to-and-fro movement. Time period = time for one oscillation.
Distance-Time Graph
Uniform speed: Distance-time graph is a straight line (linear). Steeper line = higher speed.
Non-uniform speed: Distance-time graph is a curved line.
Object at rest: Horizontal straight line (distance doesn't change).
Odometer and Speedometer
Odometer: Measures total distance travelled by a vehicle.
Speedometer: Shows the speed of a vehicle at any instant.
Summary
Speed is distance divided by time. Uniform motion has constant speed; non-uniform has varying speed. Time is measured using periodic events. A pendulum's time period depends on its length. Distance-time graphs show motion patterns visually.
Important Terms
- Speed: Distance per unit time (m/s or km/h)
- Uniform motion: Constant speed, straight line graph
- Non-uniform motion: Changing speed, curved graph
- Oscillation: One complete to-and-fro motion
- Time period: Time for one complete oscillation
Quick Revision
- Speed = Distance / Time (m/s or km/h)
- 1 km/h = 5/18 m/s
- Uniform motion → straight line on distance-time graph
- Pendulum time period depends on length, not mass
- Odometer = distance, Speedometer = speed